Highly stable LiTa2PO8-based hybrid solid electrolytes via the in situ interfacial formation technique for solid-state lithium-metal batteries

Abstract

Solid-state lithium metal batteries (SSLMBs) that incorporate composite polymer electrolytes have gained significant attention as potential replacements for liquid electrolytes (LEs) in lithium metal batteries (LMBs) due to their exceptional safety, outstanding energy storage performance, and remarkable stability even under high temperature conditions. In this study, a novel LiTa₂PO₈ (LTPO) Li⁺-ion conducting material was synthesized via the solid-state method using a 3D mixer. The LTPO powder was uniformly dispersed within polymer matrices, thereby enabling the synthesis of a hybrid solid electrolyte membrane (denoted as LTPO-HSE) through a straightforward solution-casting technique. The room-temperature total ionic conductivity (σ_t) of the LTPO pellet, 1LTPO-HSE membrane (1 : 1 polymer to LTPO ratio) and after the incorporation of 10 μL liquid electrolyte (LE) namely, 1 M lithium difluoro(oxalato)borate (LiDFOB) and 1 wt% lithium difluorophosphate (LiDFP) in ethylene carbonate/dimethyl carbonate (EC/DMC) (1 : 1 vol%) denoted as (LE-1LTPO-HSE) were approximately 0.17, 0.59 and 1.17 mS cm⁻¹, respectively. The addition of 10 μL LiDFOB and LiDFP salt-containing LE to the cathode sides improved the interfacial wettability and stability of the cathode–electrolyte interface (CEI) and solid electrolyte interface (SEI) layer formation. A 2032-type coin battery with an LiFePO₄ (LFP) cathode was cycled at 1C/1C between 2.5 and 4.0 V at room temperature and an average coulombic efficiency of 99.98% with a capacity retention of 92.3% after 800 cycles was achieved. The maximum specific capacity at the 19^th and 800^th cycles was 138 and 127.4 mA h g⁻¹, respectively. Furthermore, at high operating temperature (45 °C), the LFP/LE-1LTPO-HSE/Li cell exhibited an initial specific capacity of 151.1 mA h g⁻¹ at a rate of 2C/2C and retained 96.7% of its capacity after 300 cycles. The LFP/LE-1LTPO-HSE/Li cell also runs for more than 1740 cycles at a high discharge rate (0.5C/2C) at room temperature and delivered a retention of more than 87%. These results illustrate the viability of utilizing a high lithium-ion conductor known as LTPO as a filler material. Moreover, the novel hybrid electrolyte composed of a polymer and ceramic exhibits a stable long-term cycling performance. This finding may serve as a foundation for the development of more advanced solid-state electrolytes in the future.